Dynamic focusing head mounted display

ABSTRACT

A conventional head-mounted display (HMDs) can display a virtual image at a fixed focus (e.g., infinite focus). If the user looks at an object that appears closer than the virtual image, then accommodation by the user&#39;s eyes will cause the virtual image to appear blurry. The HMDs disclosed herein include a dynamic electro-active focusing element that changes the focus of the virtual image to account for accommodation by the user. This dynamic electro-active focusing element may include a curved layer of electro-active material, such as nematic or bi-stable (e.g., cholesteric) liquid crystal, disposed between a static concave mirror and a convex surface on a beam splitter or other optical element. Changing the refractive index of the electro-active material causes the focus of the dynamic electro-active focusing element, making it possible to shift the virtual image&#39;s focus in as the user&#39;s eyes change focus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a bypass continuation of International ApplicationPCT/US2016/059346, which was filed on Oct. 28, 2016, and which claimsthe priority benefit of U.S. Application No. 62/270,896, which was filedon Dec. 22, 2015. Each of these applications is incorporated herein byreference in its entirety for all purposes.

BACKGROUND

Head mounted displays (HMDs) are devices worn on or about the head forthe user to see information. The information seen can be either overlaidupon the images being observed in the real world (sometimes referred toas augmented reality), information presented that excludes the images ofthe real word (sometimes referred to as virtual reality), orcombinations of these (sometimes referred to as virtual/augmented, ormixed reality).

Typically, the information-bearing images presented in today's HMDs areset to a single focus point. The most common focus point is infinity, or“far distance.” This allows the user to see the information images infocus simultaneously with distant real-world objects in the case ofaugmented reality applications and see only the information at a fardistance in the case of virtual reality.

When the information-bearing images are presented to the user in the HMDat infinite focus, several problems arise. If the information-bearingimages (also called virtual images) are set to far distance focus whenusing augmented reality, a user may wish to shift their gaze to anobject that is nearer, for example, a hand-held item, which then causesthe virtual images to appear out of focus. This could happen if the userlooks at a hand-held tablet at normal reading distance. If the user'seyes can accommodate, they will change focus to bring the tablet intofocus, but since the virtual images are set to far distance focus thevirtual image will appear out of focus while the tablet image is infocus. In this case, it would be desirable if the virtual images couldbe refocused to the same distance as the tablet so that the virtualimages and the tablet are in focus simultaneously.

Similar problems occur when displaying an information-bearing image withan HMD to view virtual reality. In order to create a realisticthree-dimensional virtual image, the focus point of the virtual imageshould be varied so that the human eye changes its focus dynamically,thereby convincing the human brain that the image is nearer or fartheraway. If the information-bearing image remains at far distance focusonly, and other means of simulating varying distance are used withoutvarying focus distance, the effect is not as realistic as if the focusdistance was also changed. It would be desirable if the virtual imagescould be refocused to varying distances dynamically to enhance thevirtual reality experience.

SUMMARY

Conventional lenses can be used to vary the focus of information-bearingimages. But conventional lenses are constructed from glass and plastic,which are relatively heavy. In addition, conventional lenses generallymust be moved with electro-mechanical actuators, such as electricalmotors, to change focus. Actuators add more weight, bulk, andcomplexity. They may also consume relatively high amounts of electricalpower, which could increase the weight, bulk, and cost of the powersource.

An electro-active lens, such as a liquid-crystal lens, disposed betweenthe eye and the image to be observed can also be used to vary the focusof the eye. Because the eye translates up and down as gaze changes,however, the electro-active lens should be much larger than the pupil ofthe eye. For example, a 6 mm pupil typically requires an optic that isapproximately 40 mm wide to provide sufficient coverage in front of theeye to allow the typical gaze angle changes to occur. Because oflimitations of optical path difference (OPD) changes that can beachieved with an electro-active lens, the electro-active lens istypically subject to optical compromises, such as layer stacking andphase wrapping, to achieve the required optical power at the desiredoptical sizes. These optical compromises usually increase powerconsumption and require higher speed switching, both of which translateto higher size, weight, and cost.

Embodiments of the present technology include a compact, efficientoptical system that can work in tandem with an HMD to change the focusof the virtual images. In some implementations, this optical system islight weight, provides sufficient optical power to compensate for theaccommodation range across a wide range of the population (e.g., about 1Diopter to about 15 Diopters), and consumes very little power. It canalso be implemented without any moving parts.

For instance, the present technology may be implemented as an HMDapparatus that includes a display, beam splitter in opticalcommunication with the display, concave reflective surface in opticalcommunication with the beam splitter, and a tunable lens disposedbetween the beam splitter and the concave reflective surface. Theconcave reflective surface could also be augmented with or replaced byanother focusing component, such as a Graded Refractive Index (GRIN)lens or Fresnel structure. In operation, the beam splitter transmitslight emitted by the display. (The beam splitter may also transmitambient light to a wearer of the HMD apparatus). The concave reflectivesurface receives the light emitted by the display and transmitted by thebeam splitter and reflects an image of the display to the wearer via thebeam splitter. And the tunable lens varies a focus of the image of thedisplay reflected to the wearer.

In some cases, the display emits light polarized along an axis parallelto an optical axis of the electro-active material, which may includenematic or bi-stable liquid crystal. Because the display emits polarizedlight, the electro-active material may be implemented as just a singlelayer of nematic liquid crystal layer instead of the two nematic liquidcrystal layers required by conventional devices. This reduces thedevice's size, weight, power consumption, cost, and complexity.

The beam splitter can define a convex surface, in which case theelectro-active material is disposed between the convex surface and theconcave reflective surface. The concave reflective surface may form atleast a portion of a ground plane in electrical communication with theelectro-active material. The HMD apparatus may also include a pluralityof electrodes, disposed between the electro-active material and theconvex surface, to apply a voltage gradient to the electro-activematerial so as to vary the variable refractive index of theelectro-active material.

In other cases, the tunable lens comprises a liquid lens having adeformable curved membrane disposed in optical communication with thebeam splitter. In these cases, the flexible membrane can define theconcave reflective surface that changes shape as fluid is pumped intoand out of a cavity defined at least in part of by the concavereflective surface.

The head-mounted display apparatus can include a controller, operablycoupled to the tunable lens, to actuate the tunable lens in response toan input from the wearer. In addition, the controller can actuate thetunable lens in response to an image on the display.

The present technology may also be implemented as a method of displayinginformation on an HMD. In one example, the HMD displays aninformation-bearing image to a wearer of the HMD at a focus selected tomatch accommodation of the wearer. The HMD may generate theinformation-bearing image at a display, transmit the information-bearingimage through an electro-active material disposed between a beamsplitter and a concave reflective surface, and reflect theinformation-bearing image to the wearer via the concave reflectivesurface and the beam splitter. The HMD may actuate the electro-activematerial so as to change the focus of the information-bearing image. Insome cases, the HMD actuates the electro-active material in response toa command from the wearer and/or in response to information in theinformation-bearing image. The HMD may also actuate the electro-activematerial in response to a signal from an accommodation sensor, which maymeasure inter-pupillary distance to determine the converging point ofgaze of the eyes, sense the wavefront of incident light, measure pupildiameter and light level, etc.

Other embodiments of the present technology include a head-mounteddisplay apparatus comprising a display, a beam splitter in opticalcommunication with the display, a concave reflective surface in opticalcommunication with the beam splitter, and a liquid crystal layerdisposed between the convex surface and the concave reflective surface.In operation, the display emits polarized light. The beam splittertransmits a portion of the polarized light emitted by the display. Theconcave reflective surface receives the portion of the polarized lighttransmitted by the beam splitter and reflects an image of the display toa wearer of the head-mounted display apparatus via the beam splitter.And the liquid crystal layer varies a focus of the image of the displayreflected to the wearer.

Still another embodiment of the present technology includes ahead-mounted display apparatus comprising a display, a beam splitter inoptical communication with the display, a liquid lens in opticalcommunication with the beam splitter, and a mirror in opticalcommunication with the liquid lens and the beam splitter. In operation,the beam splitter transmits light emitted by the display. The liquidlens provides a variable optical power. And the mirror receives thelight emitted by the display and transmitted by the beam splitter viathe liquid lens and reflects an image of the display to a wearer of thehead-mounted display apparatus via the liquid lens.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided suchconcepts are not mutually inconsistent) are contemplated as being partof the inventive subject matter disclosed herein. In particular, allcombinations of claimed subject matter appearing at the end of thisdisclosure are contemplated as being part of the inventive subjectmatter disclosed herein. It should also be appreciated that terminologyexplicitly employed herein that also may appear in any disclosureincorporated by reference should be accorded a meaning most consistentwith the particular concepts disclosed herein.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The skilled artisan will understand that the drawings primarily are forillustrative purposes and are not intended to limit the scope of theinventive subject matter described herein. The drawings are notnecessarily to scale; in some instances, various aspects of theinventive subject matter disclosed herein may be shown exaggerated orenlarged in the drawings to facilitate an understanding of differentfeatures. In the drawings, like reference characters generally refer tolike features (e.g., functionally similar and/or structurally similarelements).

FIG. 1 is a profile view of a conventional birdbath optic for ahead-mounted display (HMD).

FIG. 2 is a profile view of a conventional birdbath optic for an HMD.

FIG. 3A is an exploded view of a variable-focus birdbath optic with acurved electro-active focusing element.

FIG. 3B is a cross-sectional view of a variable-focus birdbath opticwith a pair of crossed electro-active, cylindrical lenses.

FIG. 3C is a perspective view of an HMD with the variable-focus birdbathoptic shown in FIG. 3A.

FIG. 4 shows a layer of conductive and insulating material patterned toform concentric ring-shaped electrodes for actuating the curvedelectro-active focusing element shown in FIG. 3A.

FIG. 5 shows another view of the layer of conductive and insulatingmaterial shown in FIG. 4.

FIG. 6 shows electrical connections between pads and electrodes in thecurved electro-active focusing element shown in FIG. 3A.

FIGS. 7A and 7B show a membrane-based dynamic focusing birdbath optic.

FIG. 8A shows a view through an HMD with a variable-focus birdbath opticwith the wearer's focus on a far object and a virtual image set toinfinite focus.

FIG. 8B shows a view through an HMD with a variable-focus birdbath opticwith the wearer's focus on a near object and the virtual image set toinfinite focus.

FIG. 8C shows a view through an HMD with a variable-focus birdbath opticwith the wearer's focus on a near object and the focus of the virtualimage matched to the user's accommodation.

DETAILED DESCRIPTION

A birdbath with a dynamic focusing element, such as an electro-activelens concave mirror, allows dynamic change of focus of the virtual imagefor compensating for accommodation or enhancing the illusion of depth.It also provides for the ability to compensate for refractive errors ofthe user, eliminating the need for the user to wear corrective lenses,such as glasses, between an HMD device and the eye when using the HMD.Such a birdbath system allows the dynamic changing of focus of thevirtual image displayed by the HMD with low power consumption and nomoving (mechanical) parts.

Applications for inventive HMD devices include, but are not limited to:map guidance while driving without having to look away from the road,performing surgery while being provided vital signs data within the samefield of view, utilizing repair and service manuals with virtualinstructive diagrams overlaid upon the actual object being repaired orserviced, improving situational awareness of military and lawenforcement personnel by allowing additional tactical information beingprovided to them while simultaneously keeping “eyes on target,” andmore.

Conventional Birdbaths for Head-Mounted Displays (HMDs)

FIG. 1 shows a conventional “birdbath” optic 100 for use with ahead-mounted display (HMD). It includes a mini display or other displaysource 5, an optic block 10, a beam splitter 25, and a concave mirror35. An information-bearing image from the mini display or other displaysource 5 enters into an optic block 10 (in this case it is solid butcould be air), and encounters a beam splitter 25. The beam splitter 25directs a portion of the light away from the eye and allows a portion ofthe light to continue its journey to a mirror 35. The mirror 35 in thisexample is a curved concave mirror that reflects an incident light ray40 at an angle, causing the light ray 40 to converge to a focus. Thelight ray 40 encounters beam splitter 25 again, which reflects theconverging light rays 45 toward the eye 50.

Because the mirror 35 is concave, the wavefront approaching the eye isalso concave, or “pre-focused,” allowing the optics of the eye (i.e.,the cornea and crystalline lens), to focus an image on the retina withthe eye fairly close to the device. If the mirror 35 was flat, acorrective optic would be required in front of the eye to assist the eyeto bring the image into focus, but the curvature of mirror 35 eliminatesthe need for a corrective optic. However, the eye should be at apredetermined distance from the device in order for the image to come into focus without accommodation. Typical predetermined distances are11-15 mm. At these distances, people feel comfortable with the device infront of their eyes.

FIG. 2 shows a birdbath optic 200 that is similar to the device 100 inFIG. 1, except that it includes a concave mirror 65 with a shorterradius of curvature than the concave mirror 35 shown in FIG. 1. Themirror's shorter radius of curvature results in the eye 50 having to becloser to the device 200 in order for the image to come into focuswithout accommodation or corrective optics. That is, FIG. 2 shows thataltering the curvature of the concave mirror 35 in a birdbath 200 altersthe focus of the virtual images provided by the birdbath 200 by changingthe convergence angle of light rays 55 and 60.

Liquid-Crystal Dynamic Focusing Mirror Birdbath for HMD

A dynamic focus birdbath includes a tunable lens, such as anelectro-active lens or liquid lens, combined with a mirror andintegrated inside of the birdbath system. Placing a lens with anadjustable focal length between the display and concave mirror in thebirdbath (e.g., over mirror 35 in FIG. 1 or mirror 65 in FIG. 2) makesit possible to vary the power of the concave mirror and the focus of thevirtual image without moving parts. This brings at least the followingimprovements to the overall system.

First, by combining the mirror with a tunable lens, the focus of theinformation-bearing image that the user sees through the dynamic focusbirdbath optic may be adjusted without affecting the focus of the realworld image that the user also sees through the dynamic focus birdbathoptic. This can be very helpful for people with accommodation remainingin their eyes.

Second, because the tunable lens works with the mirror such that thelight passes through the lens on the way toward the mirror, and thenagain after it has been reflected, the lens retards the light twice,effectively doubling the its optical power range. This reduces powerconsumption, device complexity, and light scattering.

Third, when implemented as a liquid crystal optic combined with aconcave mirror inside of the birdbath optic and used with a displayengine that emits a polarized output, only a single layer of nematicliquid crystal or other polarization sensitive material is needed,reducing complexity, cost, power consumption, and light loss.Conversely, if the dynamic compensating liquid crystal optics werearranged in a single-pass geometry, each compensating element mightrequire two layers of liquid crystal (one for each polarization state)because the incident ambient light is not necessarily polarized. Adevice with two separate compensating lenses has up to four liquidcrystal layers, with each compensating lens having two orthogonallyaligned layers of nematic liquid crystal. Each compensating lens has twoorthogonally aligned liquid crystal layers because nematic liquidcrystal can alter one polarization state at a time. To act onunpolarized light, a beam splitter or pair of polarizers in thecompensating lens resolves the unpolarized light into orthogonalpolarization states that can be modulated by the nematic liquid crystallayers. This ensures both that light in both polarization states isaltered simultaneously. In contrast, a birdbath optic with anelectro-active concave mirror could be implemented with a single liquidcrystal layer that focuses polarized light coming from the displayengine and is not required to focus unpolarized light coming from thereal world.

FIG. 3A shows in cross section an exemplary construction of avariable-focus birdbath optic 300 with a liquid crystal based,dynamically adjustable concave mirror 310. Like the birdbaths shown inFIGS. 1 and 2, the birdbath optic 300 in FIG. 3A includes a display 5and an optic block 10 that defines a beam splitter 25 and a transparentconvex surface 70. Unlike the conventional birdbath optics, however, thebirdbath optic 300 includes several layers sandwiched between thetransparent convex surface 70 and a concave reflective layer 100.Together, these layers form the liquid crystal based, dynamicallyadjustable concave mirror 310.

As shown in FIG. 3A, the transparent convex surface 70 is coated with alayer 75 of (substantially) transparent electrically conductivematerial, such as a 40 nm thick layer of indium tin oxide (ITO). Layer80 is an alignment layer, such as rubbed polyimide. Layer 85 is a layerof liquid crystal material, for example, a 15-micron thick layer ofMerck MLC-2140. Layer 90 is another alignment layer, which could also berubbed polyimide.

Layer 95 includes electrically conductive and insulating materialspatterned to form electrodes for actuating the liquid crystal material.For example, layer 95 may be patterned into a series of concentricconductive rings, e.g., as described in greater detail below withrespect to FIGS. 4-6. Layer 95 could also include electrodes patternedin different shapes, including orthogonally positioned and stackedlinear electrodes that individually produce cylinder optical power andin combination produce spherical power. Layer 95 could also be patternedto form individually addressable pixelated areas (pixels), each of whichacts individually to produce piston-only retardation. These pixels canbe actuated collectively to produce spherical, cylindrical, or arbitrarywavefront shapes.

The concave reflective layer 100 forms a reflective surface and can bemade of or include aluminum or another suitable reflective material.Surface 105 is an end cap that traps layers 75 through 100 betweensurfaces 105 and 70. At the periphery of each of the layers describedabove is a sealing material (not shown), such as Norland 65 or anotheradhesive, to prevent the liquid crystal from escaping or leaking out.

Each layer sandwiched between the transparent convex surface 70 and theconcave reflective layer 100 can have a uniform thickness or a thicknessthat varies with distance from the optical axis of the liquid crystalbased, dynamically adjustable concave mirror 310. In other words, thetransparent convex surface 70 and the concave reflective layer 100 canhave the same radius of curvature or different radii of curvature. In adynamically adjustable concave mirror 310 with a single electrodeconfigured for a positive optical power, for example, the liquid crystallayer 85 may be thicker at the center of the dynamically adjustableconcave mirror 310 and thinner at the edges of the dynamicallyadjustable concave mirror 310. The liquid crystal layer 85 may includenematic, cholesteric, or other bi-stable liquid crystal material. Inthis case, the concave reflective layer 100 has a smaller radius ofcurvature than the transparent convex surface 70. For a lens withnegative optical power the reverse would be the case, i.e., the liquidcrystal layer 85 is thinner in the center and thicker at the edges.

In a dynamically adjustable concave mirror 310 with multiple electrodes,the liquid crystal layer 85 may be thicker at the center of thedynamically adjustable concave mirror 310 and thinner at the edges ofthe dynamically adjustable concave mirror 310 to bias the optical powerto having more plus power. For example, instead of being capable ofadjusting from zero to 3 Diopters in infinite steps, it may then bedesigned to adjust from zero to one diopter in one discrete jump, thenadjust from 1 to 4 Diopters in infinite steps. In this case, the concavereflective layer 100 has a smaller radius of curvature than thetransparent convex surface 70. Reversal of this configuration, i.e.,with an electro-active element that is thinner in the center than theedges, would bias the lens toward having more negative optical power.

The radii of curvature of the concave reflective layer 100 and thetransparent convex surface 70 also depend on the desired focal length ofthe dynamically adjustable concave mirror 310. As well understood in theart of optics, the focal length of a concave mirror is given by:

${\frac{1}{s_{0}} + \frac{1}{s_{1}}} = {\frac{2}{R} = \frac{1}{f}}$

where s₀ is the object distance from the mirror, s₁ is the imagedistance from the mirror, R is the mirror's radius of curvature, and fis the mirror's focal length. Generally speaking, the radii of curvatureof the concave reflective layer 100 and the transparent convex surface70 may be selected according to this formula such that the objectdistance can be anywhere from 2 mm to infinity and the image distancecan be anywhere from 2 mm to infinity. When adding a dynamic liquidcrystal lens to a curved mirror, the curved mirror's new, adjusted focallength can be calculated by adding or subtracting to the resultant focallength the influence of the liquid crystal's effect upon the light raystravel toward and away from the mirror. For example, if the fixed mirrorproduces 10 Diopters of optical power (i.e., a focal length of 100 mm),and the liquid crystal lens adds two Diopters of plus optical power(i.e., a focal length of 500 mm), the new focal length is 12 Diopters(i.e., a focal length of 83.3 mm).

FIG. 3B shows a birdbath optic 301 a pair of crossed liquid crystallenses 311 a and 311 b (collectively, liquid crystal lenses 311) thatprovide variable cylindrical power along orthogonal axes. Each liquidcrystal lens 311 includes a corresponding liquid crystal layer 385 a/385b sandwiched between a corresponding pair of alignment layers 380 a/380b and 390 a/390 b. And each liquid crystal layer 385 a/385 b may includenematic liquid crystal material or cholesteric or other bi-stable liquidcrystal material. A common ground plane 395 is disposed between thealignments layers 390 a/390 b. Each liquid crystal lens 311 alsoincludes a set of linear electrodes 375 a/37 b. As shown in FIG. 3B,these sets of linear electrodes 375 a/375 b are crossed. In thisexample, linear electrodes 375 a are arrayed parallel to they axis andlinear electrodes 375 b are arrayed parallel to the z axis. Generally,the linear electrodes can be arrayed in any pair of orthogonaldirections in a plane perpendicular to the birdbath optic's optical axis(the x axis in FIG. 3B).

Together, the crossed, dynamically adjustable lenses 311 providecylindrical optical powers that can be adjusted independently byapplying an appropriate waveform to the electrodes. The optical powersmay be chosen to produce a net spherical optical power or to produce adesired amount of astigmatism, e.g., to compensate for astigmatism inthe user's eye or elsewhere in the optical train.

Those of skill in the art will readily appreciate that the birdbathoptic 300 can include more or fewer components. For example, the liquidcrystal based, dynamically adjustable concave mirror 310 may includemore or fewer layers, including an additional layers of liquid crystaland electrodes. The layers may also be arranged in different orders. Andthe entrance and exit windows of birdbath optic 300 may be coated withpolarizing filters to reduce glare, anti-reflection coatings, and/orscratch coatings.

Those of skill in the art will also appreciate that the variable opticalpower provided by the electro-active lenses shown in FIGS. 3A and 3B canbe provided instead or in addition by other types of devices. Forinstance, an electro-active lens may include a reflective Fresnel lens,e.g., as disclosed in U.S. Pat. No. 9,329,309, which is incorporatedherein by reference in its entirety. Likewise, the liquid crystalportion of each electro-active lens may be implemented as s graded-index(GRIN) liquid crystal lens, diffractive liquid crystal lens, liquidcrystal lens with floating electrodes, variable liquid crystal thicknesslens, varied alignment layer strength liquid crystal lens, variedpolymer network density liquid crystal lens, or varied photoalignmentexposure liquid crystal lens. If implemented as a GRIN lens, theelectro-active lens may have powering electrodes variably spaced awayfrom the liquid crystal, a high dielectric constant insulation layer andhole patterned electrodes, a thick insulation layer and hole patternedelectrodes, a high resistance conductive layer, or hole and ring-basedelectrodes. The electro-active lens may also be implemented as a bluephase polarization insensitive lens, a dark conglomerate phasepolarization insensitive lens, a twisted nematic (TN) liquid crystaltransmission-based Fresnel zone plate, or a spatial light modulator(SLM) adaptive optics system.

Control of a Dynamically Adjustable Concave Mirror

The birdbath optic 300 shown in FIG. 3A also includes other elementsabsent from conventional birdbath displays, namely, an electronicsassembly 325 with a controller 315 and an optional antenna 320. Thiselectronic assembly 325 may be mounted inside a housing 335, shown aspart of an HMD 302 in FIG. 3C, that can also contain the display source5 as well as a power supply and any other electronics. For instance, thehousing 335 may also hold a sensor 340 that detects ambient lightlevels, movement, range, or any other parameter that can be used toactuate the birdbath optic 300 and/or the display source 5.

In operation, the controller 315 controls the focus of theinformation-bearing image (virtual image) by varying the voltage appliedto the liquid crystal layer 85 via the electrodes (described below withrespect to FIGS. 4-6). The variation can be binary (e.g., near or far),stepped through a range of positions (e.g., infinite focus, focus at 2meters, focus at 1 meter, focus at 50 cm, focus at 25 cm, etc.), orcontinuously variable over a particular range (e.g., infinite focus to25 cm) depending on the electrodes, controller 315, and user interfacefor controlling the focus.

In some cases, the controller 315 changes the focus of theinformation-bearing image in response to a signal received by theantenna 320, e.g., from a separate device used by the wearer to controlthe birdbath optic 300. For instance, the wearer may transmit a wirelesscontrol signal (e.g., a Bluetooth or Wifi signal) to the controller 315from a smart phone, smart watch, fob-style controller, or other suitabledevice.

The wearer may also adjust the focus of the information-bearing image bypressing a button or swiping an area 345 on the temple or frame of thehead-mounted display 302 to which the birdbath optic 300 is attached.Touching the button once or swiping the area 345 in a first directionmay bring the focus closer, and touching the button twice or swiping thearea in a second direction may move the focus farther away.

The controller 315 may also vary the focus of the information-bearingimage based on the information-bearing image itself. In these cases, thecontroller 315 may also be operably coupled to and control the display 5and/or be operably coupled to and receive control signals from aprocessor (not shown) that controls the display 5. If the display 5shows information intended to be seen at near focus, such as informationabout products on the shelf in the grocery store, the controller 315 mayautomatically cause the information-bearing image to appear at nearfocus. Similarly, if the display 5 shows information intended to be seenat infinite focus, such as information about the next exit on a highway,the controller 315 may automatically cause the information-bearing imageto appear at infinite focus. Note that the wearer may indirectly controlthe focus of the information-bearing image by viewing different types ofinformation via the birdbath optic 300.

The controller 315 may also respond to anatomical triggering. Forinstance, it may sense accommodation based on signals fromphotodetectors (e.g., sensor 340 in FIG. 3C) that sense ambient lightlevel levels and/or pupil diameter. It may also sense the position ororientation of the wearer's head based on signals from an accelerometerand/or a gyroscope. If the controller 315 senses that the wearer islooking down based on the accelerometer and/or gyroscope signals, it maybring the information-bearing image to near focus. And if the controller315 senses that the wearer is looking up based on the accelerometerand/or gyroscope signals, it may bring the information-bearing image toinfinite focus. The controller 315 may also be configured to vary thefocus of the information-bearing image based on electrical detection ofnervous impulses or brain waves.

Electrodes for a Dynamically Adjustable Concave Mirror

FIGS. 4 and 5 illustrate the electrode layer 95 in greater detail. FIG.4 shows an end-on view of layer 95 as it may be positioned uponreflective layer 100, which is positioned upon end cap 105. The point ofview illustrated in FIG. 4 is that of looking at the end cap into itsconcave surface. Comprising part of the electrode layer 95, a series ofconcentric electrodes 110 made from an electrically conductive butoptically transparent material are patterned onto layer 100. On top ofthe electrodes 110 is an electrically insulating layer (not shown) thatcovers the electrodes and the gaps between them. Holes 115 patternedinto the insulating layer expose a small area of each of the electrodes110 as shown in FIG. 5. The insulating layer can be silicon dioxide,which is typically 240 nm thick, or any other electrically insulating,substantially transparent material that can be processed usingelectronics lithography.

FIG. 6 shows a series of seven bus lines 120 connecting seven holes 115(labeled in FIG. 5) to seven electrical connection pads 125. With thisconfiguration, electrical power can be applied to each pad 125, and thecurrent flows to the corresponding electrode 110 without shortcircuiting as the bus line 120 passes over top of the other electrodes110. The bus lines 120 and pads 125 can be formed from nickel or anothersuitable conductive material, e.g., sputtered to a thickness of about120 nm.

To change the focus of the electro-active concave mirror, a voltagepotential is applied to each of the electrodes in a gradient fashion,with the opposite side of the circuit connected to the ground plane(layer 75). An exemplary voltage profile may be 0.6, 0.7, 0.8, 0.95,1.2, 1.55 and 1.9 volts, from the center to the outside electroderespectively. This voltage profile adds optical power to the reflectivesurface. Reversing the sequence of the voltages (for example, 1.9, 1.55,1.2 0.95, 0.8, 0.7 and 0.6 volts, from the center to the outsideelectrode, respectively) reduces the total optical power of the lens.This allows the user to make the virtual image appear closer (usingpositive optical power) or farther away (using negative optical power).

In this exemplary embodiment, the patterned electrodes are at layer 95and the ground plane is layer 75. However, by reversing the two suchthat the ground plane is at layer 95, layer 95 may be combined withreflective layer 100 and serve as both the optically reflective surfaceand the electrical ground plane, reducing complexity and cost.

In this exemplary embodiment, there are seven electrodes. Depending onthe design, using more electrodes may produce a higher quality opticalresult. For example, a typical, high quality design may utilize onehundred or more electrodes in a lens with a diameter of 10 mm across.Likewise, FIGS. 4-6 show circular electrodes, but other shapes could beused, including linear electrodes configured to produce two cylinderlenses placed orthogonal to each other to provide spherical opticalpower with variable astigmatism.

The dynamically adjustable concave mirror 310 illustrated in FIGS. 3-6includes multiple electrodes that can create a gradient in the index ofrefraction of a liquid crystal layer. This gradient focuses lightincident on the liquid crystal layer. Those of ordinary skill in the artwill readily appreciate that other techniques can be used to vary theoptical power of a concave mirror. For instance, a dynamicallyadjustable concave mirror may include a layer of electro-optic polymeror crystal whose refractive index changes in response to an appliedstress, strain, or electromagnetic field.

Liquid-Lens Dynamic Focusing Mirror Birdbath for HMD

Alternatively, the reflective surface may be formed on a flexiblemembrane that, together with the convex surface of the birdbath, definesa sealed cavity. Pumping index-matching fluid into the sealed cavitycauses the membrane to bulge, changing the focal length of thedynamically adjustable concave mirror. Withdrawing the fluid from thecavity relieves the bulge, returning the focal length to its originalvalue. The flexible membrane can also be actuated electro-statically,piezo-mechanically, thermally, or using any other suitable technique.

FIGS. 7A and 7B illustrate a birdbath 700 with a membrane-based dynamicfocusing mirror 710. The membrane-based dynamic focusing mirror 710includes a deformable curved membrane 720 disposed opposite atransparent, rigid wall 725. The curved membrane 720 is reflective orcoated in a reflective coating to reflect incident light towards thetransparent, rigid wall 725. Together, the curved membrane 720 and thetransparent, rigid wall 725 define a cavity 721 that is in fluidcommunication with a fluid reservoir 705 via an aperture 730 and afluidic channel 709. The membrane-based dynamic focusing mirror 710 alsoincludes a pump 706 that is coupled to the fluid reservoir 705 (andcould alternatively be coupled to another portion of the fluid path).And the birdbath 700 includes a controller 715 that controls the pump706.

In operation, the controller 715 actuates the pump 706 in response tosignals from the antenna 320, sensor 340, switch (e.g., user-activatedarea) 345, etc. The pump 706 responds to the actuation signal from thecontroller 715 by pumping transparent fluid 707 between the fluidreservoir 705 and the cavity 721. For example, the pump 706 may forcefluid 707 into the cavity 721, thereby causing the curved membrane 720to move away from the transparent, rigid wall 725 as shown in FIG. 7A.This reduces the focusing mirror's radius of curvature and increases itsoptical power. Similarly, the pump 706 may also force fluid 707 out ofthe cavity 721, thereby causing the curved membrane 720 to move towardsfrom the transparent, rigid wall 725 as shown in FIG. 7B. This increasesthe focusing mirror's radius of curvature and decreases its opticalpower. The exact change in optical power depends on the amount andpressure of the fluid in the cavity 721 and can be controlled in acontinuous (analog) or stepped (digital) fashion by the controller 715.

Those of skill in the art will readily appreciate that a birdbath opticthat can focus to compensate for accommodation can be implemented withmany types of liquid-based lenses in addition to the pump-based fluidicshown in FIGS. 7A and 7B. For instance, it can be implemented with anelectro-wetting lens that uses oil, saline, and/or other fluids toprovide a variable optical power. And it can be implemented with anelectronically controlled shape distorting capsule lens.

Viewing Virtual Images Through a Dynamically Adjustable Concave Mirror

FIGS. 8A-8C illustrate real and virtual images as seen, by a wearerwhose eyes accommodate, through a head-mounted display with a birdbathoptic that includes a dynamically adjustable concave mirror like thoseshown in FIGS. 3A, 7A, and 7B. FIG. 8A shows a view of what the wearersees when looking through the birdbath optic at objects 805 a at or nearinfinite focus. The objects 805 a at infinite focus appear sharply infocus, whereas closer objects, such as the wine bottle 801 a at bottomleft, appear blurry or fuzzy. Because the wearer's eyes are focused onthe far objects 805 a, the dynamically adjustable concave mirror is setto produce virtual images 803 a (here, object labels) at infinite focusthat also appear sharply in focus.

FIG. 8B shows a view of what the wearer sees when looking through thebirdbath optic at near objects without a change in the focus of thevirtual images. In this case, the wine bottle 801 b and other objects inthe foreground appear sharply in focus, whereas objects 805 b in thebackground appear blurry or out of focus. Because the wearer's eyesaccommodate, any information-bearing images 803 b at infinite focus alsoappear blurry or out of focus. (As mentioned above, a conventionalbirdbath optics cannot account for accommodation, so theinformation-bearing images that it displays may appear out of focus to awearer whose focus changes.)

FIG. 8C shows a view of what the wearer sees when looking through thebirdbath optic at near objects with a change in the focus of the virtualimages. Again, the wine bottle 801 c and other objects in the foregroundappear sharply in focus, and objects 805 c in the background appearblurry or out of focus. In this case, however, the birdbath optic focusis selected to generate the information-bearing images 803 c at nearfocus so that they also appear sharply in focus. This selection may bemade by the user via an actuator on or coupled to the birdbath optic ora remote control, such as a smart phone, smart watch, or purpose-builtdevice. The birdbath optic may also automatically adjust the focus inresponse to a signal from the display controller, possibly based on theinformation being displayed, or in response to detection of ananatomical cue, such as a change in pupil diameter absent a change inambient light level.

CONCLUSION

While various inventive embodiments have been described and illustratedherein, those of ordinary skill in the art will readily envision avariety of other means and/or structures for performing the functionand/or obtaining the results and/or one or more of the advantagesdescribed herein, and each of such variations and/or modifications isdeemed to be within the scope of the inventive embodiments describedherein. More generally, those skilled in the art will readily appreciatethat all parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the inventive teachingsis/are used. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific inventive embodiments described herein. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, inventive embodiments may be practicedotherwise than as specifically described and claimed. Inventiveembodiments of the present disclosure are directed to each individualfeature, system, article, material, kit, and/or method described herein.In addition, any combination of two or more such features, systems,articles, materials, kits, and/or methods, if such features, systems,articles, materials, kits, and/or methods are not mutually inconsistent,is included within the inventive scope of the present disclosure.

The above-described embodiments can be implemented in any of numerousways. For example, embodiments of designing and making the technologydisclosed herein may be implemented using hardware, software or acombination thereof. When implemented in software, the software code canbe executed on any suitable processor or collection of processors,whether provided in a single computer or distributed among multiplecomputers.

Further, it should be appreciated that a computer may be embodied in anyof a number of forms, such as a rack-mounted computer, a desktopcomputer, a laptop computer, or a tablet computer. Additionally, acomputer may be embedded in a device not generally regarded as acomputer but with suitable processing capabilities, including a PersonalDigital Assistant (PDA), a smart phone or any other suitable portable orfixed electronic device.

Also, a computer may have one or more input and output devices. Thesedevices can be used, among other things, to present a user interface.Examples of output devices that can be used to provide a user interfaceinclude printers or display screens for visual presentation of outputand speakers or other sound generating devices for audible presentationof output. Examples of input devices that can be used for a userinterface include keyboards, and pointing devices, such as mice, touchpads, and digitizing tablets. As another example, a computer may receiveinput information through speech recognition or in other audible format.

Such computers may be interconnected by one or more networks in anysuitable form, including a local area network or a wide area network,such as an enterprise network, and intelligent network (IN) or theInternet. Such networks may be based on any suitable technology and mayoperate according to any suitable protocol and may include wirelessnetworks, wired networks or fiber optic networks.

The various methods or processes (e.g., of designing and makingtechnology disclosed above) outlined herein may be coded as softwarethat is executable on one or more processors that employ any one of avariety of operating systems or platforms. Additionally, such softwaremay be written using any of a number of suitable programming languagesand/or programming or scripting tools, and also may be compiled asexecutable machine language code or intermediate code that is executedon a framework or virtual machine.

In this respect, various inventive concepts may be embodied as acomputer readable storage medium (or multiple computer readable storagemedia) (e.g., a computer memory, one or more floppy discs, compactdiscs, optical discs, magnetic tapes, flash memories, circuitconfigurations in Field Programmable Gate Arrays or other semiconductordevices, or other non-transitory medium or tangible computer storagemedium) encoded with one or more programs that, when executed on one ormore computers or other processors, perform methods that implement thevarious embodiments of the invention discussed above. The computerreadable medium or media can be transportable, such that the program orprograms stored thereon can be loaded onto one or more differentcomputers or other processors to implement various aspects of thepresent invention as discussed above.

The terms “program” or “software” are used herein in a generic sense torefer to any type of computer code or set of computer-executableinstructions that can be employed to program a computer or otherprocessor to implement various aspects of embodiments as discussedabove. Additionally, it should be appreciated that according to oneaspect, one or more computer programs that when executed perform methodsof the present invention need not reside on a single computer orprocessor, but may be distributed in a modular fashion amongst a numberof different computers or processors to implement various aspects of thepresent invention.

Computer-executable instructions may be in many forms, such as programmodules, executed by one or more computers or other devices. Generally,program modules include routines, programs, objects, components, datastructures, etc. that perform particular tasks or implement particularabstract data types. Typically, the functionality of the program modulesmay be combined or distributed as desired in various embodiments.

Also, data structures may be stored in computer-readable media in anysuitable form. For simplicity of illustration, data structures may beshown to have fields that are related through location in the datastructure. Such relationships may likewise be achieved by assigningstorage for the fields with locations in a computer-readable medium thatconvey relationship between the fields. However, any suitable mechanismmay be used to establish a relationship between information in fields ofa data structure, including through the use of pointers, tags or othermechanisms that establish relationship between data elements.

Also, various inventive concepts may be embodied as one or more methods,of which an example has been provided. The acts performed as part of themethod may be ordered in any suitable way. Accordingly, embodiments maybe constructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of” or, when used inthe claims, “consisting of” will refer to the inclusion of exactly oneelement of a number or list of elements. In general, the term “or” asused herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of” or“exactly one of” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

1. A head-mounted display apparatus comprising: a display; a beamsplitter, in optical communication with the display, to transmit lightemitted by the display; a concave reflective surface, in opticalcommunication with the beam splitter, to receive the light emitted bythe display and transmitted by the beam splitter and to reflect an imageof the display to a wearer of the head-mounted display apparatus via thebeam splitter; and a tunable lens, disposed between the beam splitterand the concave reflective surface and having a variable optical power,to vary a focus of the image of the display reflected to the wearer. 2.The head-mounted display apparatus of claim 1, wherein the display isconfigured to emit light polarized along an axis perpendicular to anoptical axis of the tunable lens.
 3. The head-mounted display apparatusof claim 2, wherein the tunable lens comprises a layer of nematic liquidcrystal material disposed between the beam splitter and the concavereflective surface.
 4. The head-mounted display apparatus of claim 2,wherein the tunable lens comprises a layer of bi-stable liquid crystalmaterial disposed between the beam splitter and the concave reflectivesurface.
 5. The head-mounted display apparatus of claim 1, wherein thebeam splitter is configured to transmit ambient light to the wearer. 6.The head-mounted display apparatus of claim 1, wherein: the beamsplitter defines a convex surface, and the tunable lens compriseselectro-active material disposed between the convex surface and theconcave reflective surface.
 7. The head-mounted display apparatus ofclaim 6, wherein the concave reflective surface forms at least a portionof a ground plane in electrical communication with the electro-activematerial.
 8. The head-mounted display apparatus of claim 6, furthercomprising: a plurality of electrodes, disposed between theelectro-active material and the convex surface, to apply a voltagegradient to the electro-active material so as to vary a refractive indexof the electro-active material.
 9. The head-mounted display apparatus ofclaim 1, wherein the tunable lens comprises a liquid lens having adeformable curved membrane disposed in optical communication with thebeam splitter.
 10. The head-mounted display apparatus of claim 9,wherein the flexible membrane defines the concave reflective surface.11. The head-mounted display apparatus of claim 1, further comprising: acontroller, operably coupled to the tunable lens, to actuate the tunablelens in response to an input from the wearer.
 12. The head-mounteddisplay apparatus of claim 1, further comprising: a controller, operablycoupled to the tunable lens and the display, to actuate the tunable lensin response to an image on the display.
 13. A method of displayinginformation on a head-mounted display apparatus, the method comprising:displaying an information-bearing image to a wearer of the head-mounteddisplay apparatus, via the head-mounted display apparatus, at a focusselected to match accommodation of the wearer.
 14. The method of claim13, wherein displaying the information-bearing comprises: generating theinformation-bearing image at a display of the head-mounted displayapparatus; transmitting the information-bearing image through a tunablelens disposed between a beam splitter and a concave reflective surface;and reflecting the information-bearing image to the wearer via theconcave reflective surface and the beam splitter.
 15. The method ofclaim 13, further comprising: actuating the tunable lens so as to changethe focus of the information-bearing image.
 16. The method of claim 15,wherein actuating the tunable lens comprises actuating theelectro-active material in response to a command from the wearer. 17.The method of claim 15, wherein actuating the tunable lens comprisesactuating the tunable lens in response to information in theinformation-bearing image.
 18. The method of claim 15, wherein actuatingthe tunable lens comprises varying a voltage applied to a liquid crystalmaterial.
 19. The method of claim 15, wherein actuating the tunable lenscomprises pumping fluid between a liquid lens and a fluid reservoir. 20.A head-mounted display apparatus comprising: a display to emit polarizedlight; a beam splitter, in optical communication with the display, totransmit a portion of the polarized light emitted by the display, thebeam splitter defining a convex surface; a concave reflective surface,in optical communication with the beam splitter, to receive the portionof the polarized light transmitted by the beam splitter and to reflectan image of the display to a wearer of the head-mounted displayapparatus via the beam splitter; and a liquid crystal layer, disposedbetween the convex surface and the concave reflective surface, to vary afocus of the image of the display reflected to the wearer.
 21. Ahead-mounted display apparatus comprising: a display; a beam splitter,in optical communication with the display, to transmit light emitted bythe display; a liquid lens, in optical communication with the beamsplitter, to provide a variable optical power; and a mirror, in opticalcommunication with the liquid lens and the beam splitter, to receive thelight emitted by the display and transmitted by the beam splitter viathe liquid lens and to reflect an image of the display to a wearer ofthe head-mounted display apparatus via the liquid lens.